The atomic helpers are supposed to take an atomic_t pointer, not a random
unsigned long pointer.  So convert atomic_clear_mask over.

While we're here, also add some nice documentation to the func.
Signed-off-by: NMike Frysinger <vapier@gentoo.org>
Cc: Arun Sharma <asharma@fb.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>